Luminaire

ABSTRACT

A luminaire applicable for use in marking and lighting airport runways and taxiways employs a refractor and two Fresnel-type condensing lenses, wherein the refractor is circular at its base and is comprised of two halves symmetric about a vertical plane of symmetry. Each refractor halve has an integrally-formed, outer, Fresnel-type lens which cooperates with one of the condensing lens to direct a narrow beam at a predetermined angle from the plane of symmetry. Intermediate the plane of symmetry and the outer Fresnel-type lenses is an array of upwardly extending lenticular prisms which spread light into a hemispherical zone of low and uniform intensity.

United States Patent 1 Dorman a [451 May 27, 1975 [73] Assignee: Corning Glass Works, Corning,

[22] Filed: Dec. 17, 1973 [21] Appl. No.: 425,140

Primary Examiner-Joseph F. Peters, Jr. Attorney, Agent, or Firm-Thomas J. McNaughton; Burton R. Turner; Clarence R. Patty, Jr.

[57] ABSTRACT A luminaire applicable for use in marking and lighting airport runways and taxiways employs a refractor and two Fresnel-type condensing lenses, wherein the refractor is circular at its base and is comprised of two halves symmetric about a vertical plane of symmetry. Each refractor halve has an integrally-formed, outer, Fresnel-type lens which cooperates with one of the condensing lens to direct a narrow beam at a predetermined angle from the plane of symmetry. Intermediate the plane of symmetry and the outer Fresnel-type lenses is an array of upwardly extending lenticular prisms which spread light into a hemispherical zone of low and uniform intensity.

22 Claims, 4 Drawing Figures PATENTEUHAY 27 ms SHEET F ig. J 50 1 LUMINAIRE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to luminaires, and more partic ularly to refractors and condensors for use therein which are capable of directing light from a location along the side of an airport taxiway or runway out onto the taxiway or runway and upwardly above the horizontal in a composite pattern having two main beams and also a generally hemispherical zone of uniform, rela tively low-intensity light immediately above and between the two main beams. 2. Prior Art In the standard, well-known elevated runway edgelight marker luminaires, as typified in U.S. Pat. Nos. 2,773,172 to Pennow, 2,021,611 to Rolph 2,155,295 and 2,332,362 to Bartow, the refractors employed therein have relatively large exterior surfaces. Due to their size and configuration, these luminaires are susceptible to frequent damage resulting from high velocity jet exhaust winds, from stone particles propelled against them and from collisions with low-lying portions of aircraft.

Another problem associated with the known standard runway marker luminaires relates to the light dis tribution pattern required of them. Runway marker luminaires must provide sufficient illumination for both adequate landing guidance and circling guidance. This latter term refers to that pattern of light which enables pilots following visual flight rules to determine the alignment of the runway relative to their direction of flight, so that they may maneuver their aircraft into a region of guidance. The region of guidance is located at the approach end of the landing strip and is pro duced by the main beams of the runway marker lights. If the runway markers do not transmit SUfflClBl'll. illumination to provide an adequate circling guidance pattern, pilots must refer to other less desirable forms of ground lighting in order to bring their aircraft into the region of guidance.

The presently known luminaires perform satisfacto rily in providing landing guidance but are not completely satisfactory in providing circling guidance. This problem is exacerbated by the fact that runway markers are operated at reduced voltage levels during nor mal weather conditions in order to render the main beams at a leval of intensity comfortable to a pilots night vision." When the standard runway markers are operated at such reduced levels, the amount of illumination rendered is not sufficient to provide circling guidance and accordingly pilots must refer to lighting other than the conventional runway lighting in order to determine their relationship to the runway.

Further, since either the inner or outer globe surface of the standard luminaire has an array of prisms, it must be pressed in a split mold, rather than a simple block mold as may be utilized to press the globe of the present invention, which not only materially reduces the cost of manufacture but also simplifies the operation. An additional problem with standard luminaires is that they can not be freely interchanged between elevated high-intensity runway markers, medium-intensity runway markers, and taxiway markers in the manner permitted by the novel luminaire of the present invention. With the present-day system, refractors of different sizes are required to be used for mediumand highintensity markers. While some medium intensity runway marker luminaires are used as make-do taxiway markers, this interchange can be discounted because the main beams of the standard runway marker luminaire are much narrower than those required of taxiway luminaires.

Relatively compact luminaires employing condensing lenses have been used in the past for lighting streets. U.S. Pat. No. 2,133,377, for instance, discloses a liminaire provided with two integrally-formed Fresnel-type lenses, two condensing lenses and an array of prisms. However, the edges of the prisms therein lie in planes substantially parallel with the optical axis of the doublet lenses, and thus only spread the light below the beams projected by the doublet lenses as is required for street lighting.

The luminaire of the present invention not only obviates the problem of providing a versatile airport lighting system for both circling guidance and landing guidance, but also provides a novel simple construction for use in both runway and taxiway lighting.

SUMMARY OF THE INVENTION The present invention relates to an improved limi naire for airport lighting including an outer refractor globe and a removable set of condensing lenses. The inner and outer surfaces of the refractor are symmetri cal about a vertical plane of symmetry, with each symmetric half including a center portion and an end portion. Each end portion has a Fresnel type lens integrally formed on its inner surface, with such lens cooperating with one of the condensing lenses to direct a narrow main beam. lntegrally formed on the inner surface of the center portion is an array of lenticular prisms which extend upwardly from near the rim on one side of the refractor, across the top and down the opposite side. When viewed in elevation perpendicular to the plane of symmetry, the top portion of the outer surface of the center section has the shape of abutting frustroconical surface portions, which communicate through central radiused portions with downwardly diverging linear sidewall portions lying in an end section. However, when viewed in elevation parallel to the plane of symmetry, the outer surface of the center section is generally semi-circular with tangential linear portions extending downwardly and outwardly from the semi-circular portion to the base.

When supplied with a central light source, the refractor alone produces two broad main beams and a hemispherical zone of uniform low-intensity light above and between said main beams. When the two condensing lenses are employed with the refractor, the same gen eral pattern is reproduced, with the exception that the main beams are more intense and relatively narrow.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in detail with reference to the accompanying drawings, in which:

FIG. 1 is a bottom plan view of the refractor and condensing lenses of the present invention.

FIG. 2 is a sectional view in elevation of the refractor and condensing lenses taken along line 22 of FIG. 1, with, however, a light source added thereto.

FIG. 3 is a sectional view in elevation of the refractor taken along line 33 of FIG. 1 but with the condensing lenses removed for clarity.

FIG. 4 is an enlarged fragmental sectional view taken along line 44 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The luminaire of the present invention includes a re fractor 8 forming an outer globe; and depending upon its intended use, the refractor may include two internally positioned condensing lenses 50, as illustrated in FIG. I. The refractor 8 comprises a central section A and a pair of opposed end sections B, and has a radially-outwardly extending annular flange or rim l2 surrounding a circular base portion 10. As shown, refractor 8 is composed of two symmetrical halves having inner and outer surfaces symmetric about a vertical plane of symmetry passing through line 33 of FIG. 1 and normal to a plane containing base 10. Each sym metric haif contains a center section A and one of said end sections B, as shown in FIG. 1.

As shown particularly in FIGS. 2 and 3, a Fresneltype lens 22 is formed on the inner surface of each end section B, with said lens having a circular central portion 24 surrounded by a horseshoe-shaped step portion 30 having an outer edge 31 concentric with the circular central portion. The inner surface of central portion 24 has a planar upper half portion 26 and a cylindrical lower half portion 28, which is cylindrical about a horizontal axis intersecting the vertical plane of symmetry passing through line 33. The outer surface of lens 22 is hemispherical above a horizontal plane passing through a geometric center 29 of the outer surface of circular central portion 24, and frustoconical below such plane.

As illustrated in FIG. 3, step portion 30 has a prism riser 32 which has an upper frustoconical portion 33 contiguous with the periphery of the upper portion 26 of the lens central portion 24 and a bifurcated lower portion which extends downwardly (and slightly outwardly to facilitate removel of the forming plunger) to form two planar surfaces 34. The inner face 36 of step portion 30 is planar above the horizontal plane passing through a geometric center 27 of the inner surface of circular central portion 24 (i.e., parallel with horizontal base and below such plane is concentrically cylindrical with cylindrical lower half portion 28 of the central lens portion. Step portion 30 may, however, com pletely surround central portion 24, rather than being of a horseshoe shape without deleteriously affecting the desired lighting pattern. The horseshoe shape of step portion 30 and the plane-cylindrical shape of central portion 24 are desirable since they aid manufacturing by allowing a plunger to be withdrawn along an axis lying within or parallel to the plane of symmetry of the refractor.

Preferably, the outer surface of each end section B is hemispherically smoothly rounded above the horizontal plane passing through the geometrical center 29 of the outer surface of central portion 24 of the Fresneltype lens 22, and has a frustoconical form below such plane. The flange [2 around the bottom of the outer surface of refractor 8 may be fastened to a support by any suitable means, such as a band-type fastening device.

As illustrated in FIGS. 2 and 3, each center section A of central section A includes an array of lenticular prisms 42 formed on its inner sruface. Each prism 42 extends up one side of said center section inner surface, across the top thereof and down the opposite side thereof. The prisms are partially convex and concave,

with the radii of all concave and convex portions preferably being equal. Each lenticular prism 42 lies in a plane which is parallel to said plane of symmetry passing through line 3-3 of FIG. I. As shown in FIG. 4, in nermost or central prism 43 is bisected by the plane of symmetry, and peak or convex portions 44 of the other outlying prisms 42 on each side of said plane are all tangent to a line intersecting said plane whereas the adjacent root or concave portions 45 are tangent to a parallel line also intersecting said plane, with both such lines also being parallel to the outer surface 49 of center section A intersected by the plane containing said parallel lines. However, vertical planes passing through the radii centers of said convex portions 44 and concave portions 45 not only intersect said portions such that a line tangent to any such portion at one of said intersections, and perpendicular to the vertical plane passing therethrough, will also be perpendicular to said plane of symmetry; but also said vertical planes bisect the curved portion of the convex portions 44 and the concave portions 45, respectfully.

Preferably, the concave and convex portions of prisms 42 communicate directly with each other on that side of each convex and concave portion facing away from the plane of symmetry passing throuh line 33. Those sides of each convex and concave portion which face toward said plane of symmetry (i.e. those closest to the plane of symmetry) are connected by a tangential straight portion 48. Each tangential straight portion 48 is tangent to the convex portion 44 at a point 46 and is tangent to the concave portion 45 at a point 47. The length of tangential straight portions 48 depends upon the radii of convex portions 44 and concave portions 45, and the slope of the outer surface 49 of center sections A. The vertical distance between points 46 and 47 will be directly proportional to the slope of the outer surface 49 of each center section A. The horizontal distance between points 46 and 47 depends only on manufacturing considerations, such as the draft necessary to withdraw the plunger which forms prisms 42. To achieve maximum refraction, tangential straight portion 48 would lie in a vertical plane.

The outer surface 49 of each pair of abutting center sections A of central section A is preferably smooth, and as noted, such surface above the horizontal plane passing through the geometrical center 29 of the outer surface of central lens portion 24 is in the form of the upper half of a pair of frustocones abutting at their bases along said plane of symmetry. Below such plane, the side walls on each side of central section A extend downwardly to form two abutting angularly disposed surfaces 52, which preferably are curved outwardly near flange 12 to form a step 13. Accordingly, each center section A may be said to be in the general shape of a vertically transversely elongated frustocone having its base edge contiguous with the plane of symmetry, with such frustoconical shape being elongated transversely toward base 10 from its intersection with said horizontal plane through the geometrical center 29 of the outer surface central lens portion 24. The configuration of prisms 42, in conjunction with the partially frustoconical shape of the outer surface of central section A, causes an extreme refraction of the source light directed thereon; and as will be discussed in more detail hereinafter, the generally hemispherical zone of light emitted by prisms 42 of both symmetric halves, merges with main beams directed by outer lenses 22.

It will be understood that the angular position of said lenses 22 on end portions B of the refractor 8, relative to the plane of symmetry, may be varied in order to direct the beams of light produced by such lenses toward different external points. For purposes of illuminating airport runways ans taxiways, the axis of said lenses will preferably form an angle of approximately 85 30 from the zenith of the globe in the plane of symmetry and or approximately 3 30" from a vetrical plane normal to the plane of symmetry, i.e. through line 2- 2 of FIG. 1. As will be readily understood by those skilled in the art, although the particular specifications of the refractor will vary with that required for different appli cations, such specifications can be readily determined according to the invention set forth herein by applying standard lighting formulas.

The luminaire preferably includes two condensing lenses 50. Each condensing lens has a central portion 62 and a step portion 64. Central portion 62 has an outer surface 66 which is aspherically shaped and an inner surface 68 which is spherically shaped. A rim 70, surrounding step portion 64, may be provided with a mounting lip or other means by which it may be securely fastened to a platform (not shown). The exact configuration of the step and central portions depends on, among other things, the particular configuration utilized for said refractor end portion lenses 22 and the distances allowable between the refractor 8 and a light source 14. Again, depending upon the various requirements needed to fulfill a particular use, the configuration of condensing lens 50 can be readily determined by those skilled in the art following the criteria set forth in the present invention and with the use of appropriate mathematical and optical laws.

When the luminaire is used for medium-intensity or high-intensity runway edgelights markers, the two condensing lenses 50 are required in order to provide two narrow, intense beams necessary for controlled runway illumination which does not hinder pilot vision. How ever, when the luminaire is merely used for taxiway markers, the refractor 8 alone is employed since broader beams are required to provide a more general less intense surface lighting. When utilized in the luminaire assembly, condensing lenses 50 collect the light rays incident thereon from light source 14 and direct such rays over outer lenses 22 for providing the intense runway illumination beams. However, the refraction of light rays from source 14 by lenses 50 causes an area of shadow about the main beams directed from outer lenses 22, such as would lie between the paths of light rays R1 and R2 depicted in FIG. 2, with the path of ray R1 being drawn without regard to prisms 42. In order to overcome this deficiency of illumination, the outlying prisms 42 in conjunction with the sloping configuration of the outer surface 49 of central section A, cause an extreme refraction of incident source light so as to fill in this area of shadow with illumination, as is illustrated by the path of light ray R3. More specifically, prism tangential straight portions 48 in combination with the sloping configuration of the outer surface 49 of center sections A cause an extreme refraction of light into this area of shadow, thus obviating the otherwise darkened area with refracted light from source 14. Accordingly, a sufficient amount of light is refracted into this area of shadow to provide a uniform distribution of lowintensity light between and immediately above the main beams directed from end sections B. It

should be noted that this pattern of low-intensity light is utilized for providing aeronautical circle guidance lighting, necessary for implementing a lighting system providing both runway marking and illumination.

The composite light distribution pattern resulting from the combination of condensing lenses 50 and refractor 8 is that of two main runway illuminating beams with a hemispherical, uniform iow-intensity circle guidance zone of light above and between the main beams. As previously mentioned, if it were not for the extreme refraction of light caused by tangential straight portions 48 of prisms 42, zones of shadow would be created above and about the end lenses 22 by the concentration effect of condensing lenses 50. Also, the substantially hemispherical zone of light emitted from center sections A of the refractor is uniform in intensity due to the combination of the sloping configuration of the outer surface 49 of the central section A and the orientation of the convex-concave configuration of prisms 42. A corollary advantage of the surface configuration of prisms 42 is the fact that light directed to any given point on said hemispherical zone appears to emanate uniformly from the exterior surface of refractor central section A. Maximum illumination of such hemispherical zone is effected, thus providing maximum visibility for circling guidance purposes. Also, minimum glare from directed observation is achieved, thus providing low intensity light suitable for taxiway and runway edgelight marking and illumination.

it also should be noted that the entire inner and outer surfaces of the refractor 8 can be formed by a plunger and block mold method of pressing, with the plunger being withdrawn along an axis lying in said plane of symmetry through line 3 3.

Further, it will be appreciated that each symmetric half produces the same light distribution pattern, which together, provides a continuous composite pattern having two main beams and a generally hemispherical zone of low-intensity light uniformly spread between and above these main beams However, each half of the refractor may be used separately or in combination with other types of refractors or with reflectors as may he desired without departing from the spirit and scope of the invention set forth herein.

Also, it will be appreciated that although the prisms 42 are only shown and described as being formed on the interior of the refractor, if desired, the exterior surface of the refractor may also be provided with fluting or prisms adapted to diffuse the light refracted by prisms 42. Moreover, prisms 42 themselves may be formed on the exterior surface of the refractor, although a smooth outer surface is preferred to not only prevent damage to the prismatic surfaces but also to prevent the collection of dirt and foreigh particles in the lens system. As previously mentioned, the axis of lens system 22 may vary as desired in both the horizontal and vertical axis depending on the intended use of the luminaire. Further, the references to vertical and horizontal planes were for purposes of orientation with respect to the illustrated embodiment only, it being understood that the various planes, while maintaining their relative orientations, may vary with respect to the designated positionments, depending on the particular use to which the luminaire is put.

Auxiliary light control elements such as shields, re flectors, and filters may be utilized as desired with this invention. Also, conventional colored glass or colored coatings may be employed as is customary in the field. For example, colored filters, positioned between condensing lenses 50 and outer lenses 22, and a light shield, positioned between light source 14 and the runway side of refractor 8, may be employed when the luminaire is used for runway marking. Further, as is customary for taxiway lighting, colored coatings may be applied to the inner surface of the refractor when the luminaire is so used for taxiway marking.

It will be appreciated by those skilled in the art that other variations may be made from the above description. Accordingly, it is intended that the scope of the present invention be limited only by the scope of the appended claims.

I claim:

1. A refractor in the general shape of two halves symmetric about a plane of symmetry, each of the refractor halves comprising:

a. an end section including an integral Fresnel-type lens; and

b. a center section in the general shape of a transversely elongated semi-frustocone having its base contiguous with the plane of symmetry, the center section including an array of lenticular prisms, the prisms having concave portions and convex por tions both lying in planes parallel to the plane of symmetry.

2. The refractor of claim 1 wherein each end section lens has an axis angularly intersecting said plane of symmetry and comprises an outer surface having a spherical upper half and a frustoconical lower half and an inner surface having a center portion and a step portion, the center portion having an upper half consisting ofa plane normal to the axis of the lens and a lower half consisting of a partial right cylinder, and the step por tion having a prism riser contiguous with the periphery of the lens center portion and a face being planar at its upper half and cylindrical at its lower half.

3. The refractor of claim 2 in which the step portion of the inner surface of each end section lens has a lower half defined by prism risers which extend downwardly and outwardly, whereby a plunger forming said end section lens may be withdrawn on an axis parallel to the plane of symmetry.

4. The refractor of claim 1 in which the center section prisms extend up one side of the center section, across the top thereof and down the opposite side thereof.

5. The refractor of claim 1 in which the sides of the convex and concave portions facing away from said plane of symmetry communicate directly with each other and the sides of the convex and concave portions facing toward the plane of symmetry are connected by a tangential straight portion.

6. The refractor of claim 1 wherein the convex and concave portions of the center section prisms are struck from equal radii.

7. The refractor of claim 1 in which the innermost, convex portion of the center section prisms lies in the plane of symmetry.

8. A luminaire for medium-intensity and highintensity bidirectional runway lighting comprising:

a. a centrally-positioned light source;

b. a refractor in the general shape of two symmetric halves symmetrical about a plane of symmetry and defined by a circular base portion, each of the refractor halves including an end portion and a center portion, each end portion having an integral Fresnel-type outer lens and each center portion being of the general shape of a vertically transversely elongated semi-frustocone having its base contiguous with the plane of symmetry, the center section having an array of lenticular prisms extending up one side of the center section, across the top thereof, and down the opposite side thereof, the convex portions and concave portions of the prisms lying in planes parallel to the plane of symmetry; and

c. two FresneHype condensing lenses, each having a center portion and a step portion, each center portion having an aspherical outer surface and a spherical inner surface, the step and center portions being adapted to collect light from said source and direct it toward the refractor end section Fresneltype lens.

9. The luminaire of claim 8 wherein each end section integral lens comprises an outer surface having a spherical upper half and a frustoconical lower half and an inner surface including a central portion and a step portion, the central portion having a planar upper half and a cylindrical lower half, and the step portion including a face having a planar upper half and cylindrical lower half.

10. The luminaire of claim 9 in which each step portion of the end section outer lenses has a prism riser contiguous with the periphery of the upper half of the outer lens central portion, and said prism riser extending downwardly and outwardly to lie in two planes adjacent the lower half of the outer lens central portion.

ll. The luminaire of claim 8 in which the convex and concave portions of the center section prisms communicate directly with each other on their sides facing away from said plane of symmetry but are connected on their sides facing said plane of symmetry by a tangential straight portion.

12. The luminaire of claim 8 in which the innermost convex portion of the lenticular prisms of the refractor center section lies in the plane of symmetry.

13. The luminaire of claim 9 wherein the convex and concave portions of the refractor center section prisms are struck from equal radii.

14. A refractor in the form of a globe for use with a luminaire, said refractor comprising a central section and a pair of opposed end sections, said refractor being capable of orientation such that a vertical plane of symmetry passing centrally through said central section divides the refractor into two symmetrical halves each comprising one of said end sections and half of said central section, said central and end sections terminating at their lower extents in a circular base portion lying within a plane perpendicular to said plane of symmetry, each of said end portions including a Fresnel-type lens formed integrally therewith, said central section having an outer upper surface portion in the form of the upper half of a pair of frustocones abutting at their bases along said plane of symmetry, a pair of abutting angularly disposed planar surfaces extend downwardly on each side of said central section from said abutting frustocones to said circular base portion, a plurality of juxtaposed lenticular prisms formed in said central section, said lenticular prisms having adjacent concave and convex portions, and the convex portion of each said prism as well as the concave portion thereof lying in planes parallel to said plane of symmetry.

15. A refractor as defined in claim 14 wherein vertical planes passing through the center of radius of each concave and convex portion of said lenticular prisms bisect the curved portion of each of said convex and concave portions, and said prisms include planar means for refracting light from a central source about peripherial portions of said Fresnel-type lenses.

16. A refractor as defined in claim 14 wherein said lenticular prisms include planar tangential portions connecting at least some of said concave and convex portions, and each said prism extends continuously from adjacent said base portion upwardly along side wall portions of said central portion, over the top of said central portion and downwardly along the opposite side wall portion thereof.

17. A refractor as defined in claim 14 wherein each of said Fresnel-type lenses comprises a circular central portion surrounded by a horseshoe-shaped step portion having an outer edge concentric with said circular central portion.

18. A refractor as defined in claim 14 wherein each of said Fresnel lenses is formed about an axis which intersects said plane of symmetry at an angle of less than 90 thereto.

19. A refractor as defined in claim 14 wherein each of said Fresnel-type lenses includes a circular central portion and a step portion adjacent thereto, said central portion having an inner surface with a planar upper half and a cylindrical lower half, said cylindrical lower half being cylindrical about a horizontal axis, and the outer surface of said central portion being hemispherical above a horizontal plane passing through a geometric center of said circular central portion and frustoconical below such plane.

20. A refractor as defined in claim 19 wherein said step portion includes a prism riser having an upper frustoconical portion contiguous with the periphery of an upper portion of said circular central portion and a lower portion which extends downwardly to form two planar surfaces, and said step portion having an inner face provided with a planar upper portion and a cylindrical lower portion concentrically cylindrical with the lower half of the inner surface of said circular central portion.

21. A luminaire for use in lighting and marking runways and taxiways which comprises, a central light source, a globe-like refractor about said light source, and means positioned between said light source and said refractor for collecting rays from said light source and directing such rays towards specific areas of said refractor, said refractor including a central section and a pair of end sections which terminate at their lower extents in a circular base portion, said end portions each including a Fresnel-type lens having a circular central portion bounded at least partially by a step portion having an outer edge concentric with said circular portion, and at least one array of lenticular prisms formed in said central section and extending from adjacent said base on one side of said refractor to adjacent the base on the opposite side thereof, each of said lenticular prisms within said array having concave and convex portions joined by planar tangential portions and said prisms each lying within a plane parallel to each other, and said means for collecting rays of light from said light source directing said rays toward said Fresnel-type lenses formed in said end sections.

22. A luminaire as defined in claim 21 wherein said means for collecting light rays from said light source and directing such rays toward said Fresnel-type lenses includes a pair of condensing lenses positioned within said globe, each of said condensing lenses having a central portion surrounded by a step portion, said central portion having an aspherically shaped outer surface facing toward one of said Fresnel-lenses and a spherically shaped inner surface facing said light source. 

1. A refractor in the general shape of two halves symmetric about a plane of symmetry, each of the refractor halves comprising: a. an end section including an integral Fresnel-type lens; and b. a center section in the general shape of a transversely elongated semi-frustocone having its base contiguous with the plane of symmetry, the center section including an array of lenticular prisms, the prisms having concave portions and convex portions both lying in planes parallel to the plane of symmetry.
 2. The refractor of claim 1 wherein each end section lens has an axis angularly intersecting said plane of symmetry and comprises an outer surface having a spherical upper half and a frustoconical lower half and an inner surface having a center portion and a step portion, the center portion having an upper half consisting of a plane normal to the axis of the lens and a lower half consisting of a partial right cylinder, and the step portion having a prism riser contiguous with the periphery of the lens center portion and a face being planar at its upper half and cylindrical at its lower half.
 3. The refractor of cLaim 2 in which the step portion of the inner surface of each end section lens has a lower half defined by prism risers which extend downwardly and outwardly, whereby a plunger forming said end section lens may be withdrawn on an axis parallel to the plane of symmetry.
 4. The refractor of claim 1 in which the center section prisms extend up one side of the center section, across the top thereof and down the opposite side thereof.
 5. The refractor of claim 1 in which the sides of the convex and concave portions facing away from said plane of symmetry communicate directly with each other and the sides of the convex and concave portions facing toward the plane of symmetry are connected by a tangential straight portion.
 6. The refractor of claim 1 wherein the convex and concave portions of the center section prisms are struck from equal radii.
 7. The refractor of claim 1 in which the innermost, convex portion of the center section prisms lies in the plane of symmetry.
 8. A luminaire for medium-intensity and high-intensity bidirectional runway lighting comprising: a. a centrally-positioned light source; b. a refractor in the general shape of two symmetric halves symmetrical about a plane of symmetry and defined by a circular base portion, each of the refractor halves including an end portion and a center portion, each end portion having an integral Fresnel-type outer lens and each center portion being of the general shape of a vertically transversely elongated semi-frustocone having its base contiguous with the plane of symmetry, the center section having an array of lenticular prisms extending up one side of the center section, across the top thereof, and down the opposite side thereof, the convex portions and concave portions of the prisms lying in planes parallel to the plane of symmetry; and c. two Fresnel-type condensing lenses, each having a center portion and a step portion, each center portion having an aspherical outer surface and a spherical inner surface, the step and center portions being adapted to collect light from said source and direct it toward the refractor end section Fresnel-type lens.
 9. The luminaire of claim 8 wherein each end section integral lens comprises an outer surface having a spherical upper half and a frustoconical lower half and an inner surface including a central portion and a step portion, the central portion having a planar upper half and a cylindrical lower half, and the step portion including a face having a planar upper half and cylindrical lower half.
 10. The luminaire of claim 9 in which each step portion of the end section outer lenses has a prism riser contiguous with the periphery of the upper half of the outer lens central portion, and said prism riser extending downwardly and outwardly to lie in two planes adjacent the lower half of the outer lens central portion.
 11. The luminaire of claim 8 in which the convex and concave portions of the center section prisms communicate directly with each other on their sides facing away from said plane of symmetry but are connected on their sides facing said plane of symmetry by a tangential straight portion.
 12. The luminaire of claim 8 in which the innermost convex portion of the lenticular prisms of the refractor center section lies in the plane of symmetry.
 13. The luminaire of claim 9 wherein the convex and concave portions of the refractor center section prisms are struck from equal radii.
 14. A refractor in the form of a globe for use with a luminaire, said refractor comprising a central section and a pair of opposed end sections, said refractor being capable of orientation such that a vertical plane of symmetry passing centrally through said central section divides the refractor into two symmetrical halves each comprising one of said end sections and half of said central section, said central and end sections terminating at their lower extents in a circular base portion lying within a plane perpendicular to said plane of symmetry, eacH of said end portions including a Fresnel-type lens formed integrally therewith, said central section having an outer upper surface portion in the form of the upper half of a pair of frustocones abutting at their bases along said plane of symmetry, a pair of abutting angularly disposed planar surfaces extend downwardly on each side of said central section from said abutting frustocones to said circular base portion, a plurality of juxtaposed lenticular prisms formed in said central section, said lenticular prisms having adjacent concave and convex portions, and the convex portion of each said prism as well as the concave portion thereof lying in planes parallel to said plane of symmetry.
 15. A refractor as defined in claim 14 wherein vertical planes passing through the center of radius of each concave and convex portion of said lenticular prisms bisect the curved portion of each of said convex and concave portions, and said prisms include planar means for refracting light from a central source about peripherial portions of said Fresnel-type lenses.
 16. A refractor as defined in claim 14 wherein said lenticular prisms include planar tangential portions connecting at least some of said concave and convex portions, and each said prism extends continuously from adjacent said base portion upwardly along side wall portions of said central portion, over the top of said central portion and downwardly along the opposite side wall portion thereof.
 17. A refractor as defined in claim 14 wherein each of said Fresnel-type lenses comprises a circular central portion surrounded by a horseshoe-shaped step portion having an outer edge concentric with said circular central portion.
 18. A refractor as defined in claim 14 wherein each of said Fresnel lenses is formed about an axis which intersects said plane of symmetry at an angle of less than 90* thereto.
 19. A refractor as defined in claim 14 wherein each of said Fresnel-type lenses includes a circular central portion and a step portion adjacent thereto, said central portion having an inner surface with a planar upper half and a cylindrical lower half, said cylindrical lower half being cylindrical about a horizontal axis, and the outer surface of said central portion being hemispherical above a horizontal plane passing through a geometric center of said circular central portion and frustoconical below such plane.
 20. A refractor as defined in claim 19 wherein said step portion includes a prism riser having an upper frustoconical portion contiguous with the periphery of an upper portion of said circular central portion and a lower portion which extends downwardly to form two planar surfaces, and said step portion having an inner face provided with a planar upper portion and a cylindrical lower portion concentrically cylindrical with the lower half of the inner surface of said circular central portion.
 21. A luminaire for use in lighting and marking runways and taxiways which comprises, a central light source, a globe-like refractor about said light source, and means positioned between said light source and said refractor for collecting rays from said light source and directing such rays towards specific areas of said refractor, said refractor including a central section and a pair of end sections which terminate at their lower extents in a circular base portion, said end portions each including a Fresnel-type lens having a circular central portion bounded at least partially by a step portion having an outer edge concentric with said circular portion, and at least one array of lenticular prisms formed in said central section and extending from adjacent said base on one side of said refractor to adjacent the base on the opposite side thereof, each of said lenticular prisms within said array having concave and convex portions joined by planar tangential portions and said prisms each lying within a plane parallel to each other, and said means for collecting rays of light from said light source directing said Rays toward said Fresnel-type lenses formed in said end sections.
 22. A luminaire as defined in claim 21 wherein said means for collecting light rays from said light source and directing such rays toward said Fresnel-type lenses includes a pair of condensing lenses positioned within said globe, each of said condensing lenses having a central portion surrounded by a step portion, said central portion having an aspherically shaped outer surface facing toward one of said Fresnel-lenses and a spherically shaped inner surface facing said light source. 